Existing ceiling fans are typically powered by high pole number AC induction motors, operating directly from the utility AC line voltage at high degrees of frequency slip, which makes operation very inefficient. Typical domestic ceiling fans may be optimised for low cost and long life, but not electrical efficiency. For example a typical domestic ceiling fan consumes around 75 W of electrical input power, but only generates around 15 W of mechanical shaft power; an efficiency of just 20%. The balance of 60 W is consumed almost entirely by electrical losses and is dissipated as heat within the motor housing.
For an AC induction motor, significant losses are incurred by generating the rotor magnetic poles, which are formed by electromagnets powered from the incoming ac line supply. While rotor losses occur in all AC induction motors, they form a higher proportion of total losses in a ceiling fan motor because of the relatively low mechanical shaft power.
In addition to consuming excessive electricity, the wasted energy is largely dissipated as heat causing substantial temperature rise within the motor, particularly at low speeds where the airflow is substantially reduced.
To keep motor temperature rise within acceptable limits, ceiling fan motors are typically provided with ventilation holes to allow airflow through the motor interior for cooling. Ventilated covers are provided external to the motor to prevent user access to live wiring, but still allowing airflow.
Since ceiling fan blades and other components are constantly exposed to circulating room air currents carrying household dust, over time dust is deposited most noticeably on the blades and on the upper motor cover. These require regular cleaning. Cleaning is more frequently required if the fan is located in a food service area where hygiene is important, and where the air may carry additional particles of grease and/or oil making removal of dust from the fan surfaces more difficult.
Dusting with a dry cloth or brush is a common method for dust removal from surfaces. However, the process of dusting contributes to airborne dust levels by disturbing dust particles from the surface and failing to capture them in the cleaning cloth. Since the ceiling fan is necessarily mounted above head height, disturbed dust particles can be spread over a wide area and thus present more potential for irritation to sufferers of asthma and allergies than if disturbed at floor level.
Various inventors have proposed solutions to this issue, including; a Ceiling Fan Cleaning Apparatus (U.S. Pat. No. 5,319,821); a Safety Blade For Ceiling Fan (U.S. Pat. No. 6,183,201); Ceiling Fan Dust Collector Cover For Blades (D341881). None of these address the issue of thoroughly cleaning the entire ceiling fan in a manner which is both safe and effective.
The amount of dust disturbed during cleaning can be greatly reduced by using a damp or wet cloth which captures the dust particles before they spread. To further aid in removal where the dust is contaminated with oil or grease particles, use of warm water and a suitable mild cleaning agent is preferred.
However traditional ceiling fan manufacturers' typically warn against using water during cleaning due to the risk of electric shock to the user, and/or damage to the motor. This restriction on wet cleaning applies even to fans specifically rated for use in damp or wet areas, since these fans are tested only for water ingress in the most typical direction for the installation, which is generally rainwater falling from above, rather than being cleaned from below.
So, there is a need for a ceiling fan which resolves these difficulties by allowing the use of water during the cleaning process, without risking damage to the fan or presenting an electrical shock risk to the user.